An oxygen sensor is used for monitoring the amount of oxygen present in the air/fuel mixture of an internal combustion engine. Oxygen sensors are part of the emissions control system of a vehicle and are typically assembled to an exhaust pipe downstream from the combustion process so that a nose of the oxygen sensor protrudes into the exhaust pipe so that it may sample the combustion gases produced by the engine. The data obtained by the oxygen sensor helps to determine the combustion efficiency of the engine air/fuel mixture. Typically, the stoichiometric air/fuel ratio theoretically necessary for complete combustion is 14.7 to one (14.7 kg of air to 1 kg of fuel). A powertrain control module (PCM) uses data obtained from the oxygen sensor to adjust the amount of air and fuel entering the engine to maintain the desired air/fuel ratio.
A complete combustion process is ideal for a number of reasons. If the combustion process involves a lower level of air (i.e., a higher level of fuel), a “rich” condition exists and not all of the raw fuel will be completely burned in the combustion chamber leading to an increase in hydrocarbon (HC) and carbon monoxide (CO) emissions from the vehicle. If the combustion process involves a higher level of air (i.e., a lower level of fuel) a “lean” condition exists and the combustions temperatures will elevate, leading to increased levels of nitrogen oxides (NOx) being emitted from the vehicle as well as a the potential to damage the engine and/or catalytic converter.
Generally, oxygen sensors must be heated to temperature prior to beginning the monitoring process. In one embodiment of a known oxygen sensor, the operational temperature of the oxygen sensor is 574 degrees Fahrenheit (° F.). Using this known sensor, while the oxygen sensor is heating to its operational temperature, the engine runs in a so-called “open loop” condition. In practice, the heating takes place using the heat of the combustion gases. As a result, during the heating process, involving actual engine combustion, the PCM does not receive any data from the oxygen sensor on the quality of the combustion gases. While the PCM may adjust the air and fuel based on its best estimates from environmental conditions, the PCM may not be able to obtain the most desired stoichiometric air/fuel ratio to optimize combustion. After the prior art oxygen sensor is brought up to temperature, the engine runs in a so-called “closed loop” condition. When in a closed-loop condition the PCM may obtain data from the oxygen sensor about the quality of the combustion gases and adjust the air/fuel mixture, accordingly.
Heating elements have been developed and added to oxygen sensors in an attempt to heat the oxygen sensor to its operational temperature without having to rely solely on the gases of combustion. The heating element is typically activated as the ignition is turned to the ON position. In practice, these types of oxygen sensors can usually be brought up to operational temperature in less time than sensors that do not have such a supplemental heating mechanism so that the PCM and engine can enter the “closed loop” condition more quickly, permitting the earlier adjustment after engine startup of the air and fuel mixture. Overall pollution related emissions are decreased. Fuel economy is improved. Moreover, powertrain durability is enhanced.
With the ever increasing requirement for vehicle-based on-board diagnostics (OBD), millions of vehicles are brought to dealerships or service stations across the world for problem diagnosis and repair. In the field of vehicle service, verifying the heater operation of an oxygen sensor is not standardized. Also, many service technicians do not fully understand the operation of oxygen sensors. Unfortunately, lack of understanding often leads to fully operational oxygen sensors being inadvertently replaced on vehicles because there is no standard for service technicians to follow. The disclosed diagnostic tool provides an innovative approach to standardizing and automating the verification of heater operation of a vehicle-based oxygen sensor used in conjunction with regulating the air/fuel ratio of combustion gases.